The field of the invention is the purification of tertiary amines and the present invention is particularly concerned with elution (separation by washing) of adsorbents with the tertiary amines dissolved in an eluent (organic solvent) followed by separation of the tertiary amines from the eluate (washing obtained by elution).
Both in the preparation of tertiary amines and in their exposure to heat in certain industrial processes, undesired by-products are formed in most cases. Their complete removal by preparative methods is either involved or impossible.
The tertiary amines being purified in the present invention are obtained, for example, from the methods of manufacture as disclosed in the Kirk-Othmer, "Encyclopedia of Chemical Technology," 2nd edition, vol. 2 (1963) pages 97-127, particularly pages 117 and 125 where the preparation of tertiary amines is disclosed and from the thermolysis of tertiary amine hydrochlorides such as is described, for example, in West German published application No. 2,633,640and in U.S. Pat. application Ser. No. 10,048.
The process of West German published application No. 2,633,640 is carried out with the following steps:
(a) aqueous hydrochloric acid is extracted with an amine or a mixture of an amine and an inert, water-immiscible solvent which boils below the amine used, the latter being tertiary alkylamines, tertiary aryldialkylamines, secondary arylalkyamines, primary alkylarylamines or mixtures thereof, which contain 14 to 36 carbon atoms in the nitrogen-bonded side chains, which side chains include at most one nitrogen-bonded methyl group and at least one aliphatic radical containing at least 6carbon atoms, the acid constant K.sub.a of the amine being less than 10.sup.-3,
(b) an inert, water-immiscible solvent which boils below the amine used is added to the extract, unless the solvent has already been added in stage (a),
(c) the extract is distilled, the resulting vapors are condensed, the water is continuously removed from the two-phase condensate, and the organic phase is returned to the distillation process, and
(d) after removing the water, the extract is distilled under reflux at temperatures of between 100.degree. and 250.degree. C. at the column bottom, and the gaseous hydrogen chloride liberated at the top of the column is taken off.
According to the method of U.S. Pat. application Ser. No. 10,048, which does not form part of the prior art, the gaseous hydrogen chloride is obtained--in a modification of the process of the West German published application--by heating the mixture of amine hyrochloride and solvent to a temperature below the boiling point of the solvent and separating off the hydrogen chloride liberated by passing an inert gas stream through the mixture.
It has been found, in the thermal cleavage of amine hydrochlorides, that tertiary amines decompose within a more or less brief period, inter alia with the formation of interfering primary and secondary amines, which amines in general also represent the essential part of the impurities encountered when tertiary amines are manufactured. These amines formed by degradation, and their hydrochlorides, must therefore also be removed before recycling the tertiary amines in order to improve the economy of the prior art processes.